The American Petroleum Institute's system of classifying crude oils includes designations by gravity, relating the oil to the density of water. By this system, a high gravity oil is one which contains a high concentration of volatile, low molecular weight hydrocarbons, and a lower gravity oil will contain fewer such components.
When a high gravity oil is recovered from the ground and placed in a tank or other vessel not equipped with a special seal or vent designed to contain or minimize vapor emissions, substantial losses of light hydrocarbons can be incurred simply from evaporation and volatilization. This not only represents an economic loss but also is environmentally undesirable; moreover, some of the volatile components—for example, benzene, toluene and xylene in the atmosphere—could be hazardous for nearby workers.
Liquid storage is also commonly provided for liquid components removed from natural gas, sometimes known as “condensates and distillates.” Although in the liquid phase at the time of removal from the produced gas, they tend to include significant concentrations of readily volatilized light hydrocarbons, which are especially vulnerable to loss.
Some tanks and other storage vessels are equipped with special seals, pressure controls, or vents made to suppress emissions not only during static storage conditions, but also when the tanks are being filled or when the contents are being removed, and otherwise when there may be a degree of turbulence in them. Variations in head space when the liquid level is low or when the vessel is near filled are of course important factors in volatilization, as are variations in temperature, which affect vapor pressures. Numerous storage tanks in the field—in the vicinity of producing wells—are not equipped with the expensive vents necessary to adjust to such variations. As seen in U.S. patent application Ser. No. 13/136,237 filed Jul. 27, 2011 by one of the inventors herein, formation of a pumpable gel in the stored hydrocarbons will inhibit undesired volatilization of the lighter hydrocarbons in storage. Presence of the gel may be undesirable, however, when the hydrocarbons are to be trucked or piped to a new location for use or further storage, perhaps temporary. A convenient method of breaking the gel to reduce the cost and difficulty of moving the high gravity oil or condensates is needed.